Solliance and ECN take major step in improving tandem solar cells

A 26.1 % efficient tandem solar cell has been demonstrated when combining this perovskite solar cell with an industrial c-Si cell.

The active area of the small semi-transparent perovskite cell is 0.09 cm2 and the power conversion efficiency 16.4 %.

Solliance has achieved major progress in perovskite technology for industrial high efficiency tandem PV by realizing a very high near infrared transparent and efficient perovskite cell. When mechanically stacked on a crystalline Silicon cell, a hybrid tandem device is obtained with an efficiency of 26.1 %. It is the first time this efficiency mark has been reached with a hybrid tandem based on a perovskite solar cell and a commercial c-Si cell from SunPower.

Dong Zhang, researcher at Solliance:

“By optimization of the ITO composition, ITO deposition conditions and careful design of the anti-reflection coatings (ARC), an extremely high transparency is achieved for the top electrode, despite the low temperature process window.”

A normal glass sheet without ARC typically has a transparency in this wavelength range of around 92%.

For ITO with a sheet resistance of 40 Ohm per square, the average transmittance of the complete perovskite cell in the relevant near infrared wavelength range (800 – 1200 nm) is 93 %, this is significantly higher than the state of the art values published for semitransparent perovskite cells, which are below 85 %.

Sjoerd Veenstra, program manager Perovskite Solar Cells at Solliance:

“Scaling up from a laboratory scale to an industrial process is one major barrier for a successful implementation of a new promising development. Therefore, Solliance employs different scales in its work programmes. Now that the device has been proven with spin coated layers, we are using pilot scale equipment provided by our industrial partners to scale it to a viable industrial production process. It has already been successfully transferred to processing by slot die coating on 6 inch substrates.”

In addition, the expertise of industrial partners of Solliance in sheet-to-sheet spatial ALD and laser interconnection of thin film cells is being employed to scale the technology up to eventually 30 cm demonstration modules.

The 26.1 % result was achieved by combining the semi-transparent top cell with a commercial 5-inch SunPower cell. The measured power conversion efficiency of the SunPower cell by itself was 23.8 % when directly illuminated. By placing the perovskite cell in front of the Silicon cell, the combined performance of top (16.4 %) and bottom (9.7 %) cells produces a 26.1 % tandem efficiency. Thus, the performance of the SunPower cell, the best c-Si solar available on the market today, is improved by an impressive 2.3 percent points (absolute).

In the International Technology Roadmap for Photovoltaics (9th edition, published March 2018), tandems based on crystalline silicon bottom cells are expected to enter the market in 2020 and subsequently quickly achieving significant market penetration. Because of the high efficiency and uniform aesthetics of four terminal tandem modules, they should be very attractive for residential applications. Significant progress in development and demonstration is therefore expected to happen in the next few years.

Solliance has presented the results at the SiliconPV conference, from March 19th to March 21st 2018, in Lausanne, Switzerland.